La-5 supercharger anomaly?

[SCG_Limboski]

I've been testing the La-5 (series 8, default loadout) and I noticed that if you engage the second stage supercharger  below the rated altitude of 3,500 meters, you lose speed DESPITE showing an INCREASE  in manifold pressure (MAP).  For example, at 2,000m with boost on and the first stage supercharger engaged, I was showing 1040mm MAP and a speed of 493 KPH.  When I switched to the second stage supercharger,  MAP increased to 1140 mm but my speed decreased to 481 KPH.  I also saw the same behavior with the M-82F engine option.

 

Is this a bug or does the second stage supercharger increase drag somehow?  I would assume more MP should always result in more power and hence more speed and not the reverse.

Edited September 24, 2019 by SCG_Limbo

[6./ZG26_Klaus_Mann]

4 minutes ago, SCG_Limbo said:

I've been testing the La-5 (series 8, default loadout) and I noticed that if you engage the second stage supercharger  below the rated altitude of 3,500 meters, you lose speed DESPITE showing an INCREASE  in manifold pressure (MP).  For example, at 2,000m with boost on and the first stage supercharger engaged, I was showing 1040mm MP and a speed of 493 KPH.  When I switched to the second stage supercharger,  MP increased to 1140 mm but my speed decreased to 481 KPH.  I also saw the same behavior with the M-82F engine option.

 

Is this a bug or does the second stage supercharger increase drag somehow?  I would assume more MP should always result in more power and hence more speed and not the reverse.

Well, a Centrifugal Type Supercharger eats more Power the more it is throttled. So you just have less Power available even at higher MAP.

[CountZero]

I think there is bug with La5 supercharger in game, spec say switch at 3,5km but in game you get better performance in combat mode if you have supercharger 1 up to 4,5km and then switch. And if your using boost youll get better performance if you switch sup 2 at 2,5km insted 3,5.

All other airplanes superchargers work as in specs, on what alt spec say thats the best to switch for max performance in game, but la5 3,5km is not best in game as spec says it should be swiched.

And then as same engine is on La5FN when in combat mode, you also have same behavior as when in boosted on La5 (switch at 2,5 insted 3,5 is better.

 

Pic showing differance if you go by specs by switching at 3,5km (red lines), or by how it works best in game ( blue lines) for la5:

 

 

Spoiler

 

Edited September 24, 2019 by 77.CountZero

[-TBC-AeroAce]

I dont know about the accuracy of the engine model. But with all planes I just read the instruments to see if I should change or not. I.e. if when I change charger do I see better boost. If not I change back. 

 

simple

Edited September 24, 2019 by AeroAce

[Nocke]

you should re-read Klaus_Mann's post ...

[-TBC-AeroAce]

2 minutes ago, Nocke said:

you should re-read Klaus_Mann's post ...

 

I would just say.. fly what u see and not what the book says!

 

If it says change charger at x height and u do not see a change in MP, change back and wait for it to give u an advantage,

 

 

[Nocke]

the supercharger needs power to compress the air. If you switch it on too early, it uses more power to do its work, than you gain from its effect.

[CSW_Hot_Dog]

Yeah, exactly how Klaus_Mann and Nocke said. That is not an anomaly, but how it actualy work on all aircrafts with two or more speed supercharger...

 

Lets see an example with made up numbers just for demonstration:

1. speed on supercharger - 1040 MaP - engine produce 1000Hp of power - supercharger consumes 200Hp so 800Hp left for the propeller

2. speed on supercharger - 1140 MaP - engine produce 1100Hp of power - supercharger consumes 400Hp so 700Hp left for the propeller

Edited September 24, 2019 by CSW_Hot_Dog

[SCG_Wulfe]

Hey Limbo, 

 

In more detail, essentially you have two gears. The first is like the lower gears on a bike or car and spins the supercharger at a reduced effort for the engine, the second stage is a higher gear and spins the supercharger faster but at an increased effort for the engine. At lower altitude where air pressure is already greater in the engine, it's naturally able to make more power with less boost, the additional power sapping that occurs when you ask the engine to turn the supercharger at a greater rate of speed (the higher gear) actually outweighs the performance gained from the boost increase. As you go higher however, this relationship changes as the engine becomes more and more air starved and the effect of pumping that little bit more air into the engine begins to outweigh the loss of power from turning the supercharger faster. 

[CSW_Hot_Dog]

1 hour ago, AeroAce said:

I dont know about the accuracy of the engine model. But with all planes I just read the instruments to see if I should change or not. I.e. if when I change charger do I see better boost. If not I change back. 

 

simple

 

Quote

I would just say.. fly what u see and not what the book says!

 

If it says change charger at x height and u do not see a change in MP, change back and wait for it to give u an advantage,

 

 

No offense, but if you do it this way, you do it wrong and you dont get maximal thrust.

Edited September 24, 2019 by CSW_Hot_Dog

[69th_Mobile_BBQ]

You may have noticed that once the manifold pressure reaches 9.5 on the dial (at ground level), it stays there.  It doesn't matter if it's (IIRC) ~70% or 100%. You're only going to get slightly more oomph on the deck running flat out vs. running the minimum throttle setting to to get 9.5 manifold.  However, what you can do is keep the minimum throttle required and keep the rest of the throttle power as 'head room'.  If you've gotten to a good cruise speed or are in a dive and need to run, then throttling up to 100% will act as a 'mini-boost' for a short time and squeeze out a few extra k/ph. 

 

it's more fuel efficient to run at the lowest throttle setting possible to achieve that 9.5 manifold dial setting.  Of course, as altitude increases so does the need to add throttle.  The supercharger 'supplements' the manifold pressure so you don't need to run 100% throttle to achieve 9.5 on the dial once you get above 3500m.

[SCG_Limboski]

Thanks guys...I understand how a supercharger works much better now!

 

On a side note, for the La-5, is there a good reason for NOT having the boost engaged all of the time? (Assuming you manage your engine well enough to avoid damage of course.)  I assume the only downside is that more fuel is consumed with it on.

[CSW_Hot_Dog]

Boost on La-5 and La-5F only open/allow higher MaP. So you are probably basically right, only more fuel consumption and more engine wear if higher MaP.

[SCG_Limboski]

7 hours ago, =AVG77=Mobile_BBQ said:

You may have noticed that once the manifold pressure reaches 9.5 on the dial (at ground level), it stays there.  It doesn't matter if it's (IIRC) ~70% or 100%. You're only going to get slightly more oomph on the deck running flat out vs. running the minimum throttle setting to to get 9.5 manifold.  However, what you can do is keep the minimum throttle required and keep the rest of the throttle power as 'head room'.  If you've gotten to a good cruise speed or are in a dive and need to run, then throttling up to 100% will act as a 'mini-boost' for a short time and squeeze out a few extra k/ph. 

 

For which plane?  On the La-5, you can reach 1140mm HG manifold pressure (MAP) on the deck as stated in the specs which is correct.

 

Edit: Okay, I see your point now.  Yes, you can run about 72% throttle and achieve 950 mm HG MAP.  In my test, I ran at the lower 70% setting and achieved a IAS of 488 KPH.  Pushing the throttle to 100% resulted in a brief 491 KPH (IAS) before returning back to 488.

 

However, running  with boost on and achieving 1080 mm HG, which can be run indefinitely until fuel runs out, I achieved a constant speed of 513 KPH.  So, you are just better off running with boost on and running a higher MAP (>950) and just adjusting rads and throttle to keep the engine from overheating based on my testing.

 

Edited September 25, 2019 by SCG_Limbo

[69th_Mobile_BBQ]

2 hours ago, SCG_Limbo said:

 

For which plane?  On the La-5, you can reach 1140mm HG manifold pressure (MAP) on the deck as stated in the specs which is correct.

 

Edit: Okay, I see your point now.  Yes, you can run about 72% throttle and achieve 950 mm HG MAP.  In my test, I ran at the lower 70% setting and achieved a IAS of 488 KPH.  Pushing the throttle to 100% resulted in a brief 491 KPH (IAS) before returning back to 488.

 

However, running  with boost on and achieving 1080 mm HG, which can be run indefinitely until fuel runs out, I achieved a constant speed of 513 KPH.  So, you are just better off running with boost on and running a higher MAP (>950) and just adjusting rads and throttle to keep the engine from overheating based on my testing.

 

Is that with the M82F mod or without?       I'll have to spend more time with the Series.8 and experiment with settings. 

[SCG_Limboski]

The M-82F is like the M-82 except that you do not have the 5 minute time limit running at 1140 mm HG MAP & 2400 RPM which is only achievable around less than 1,000 m and running boost.  The test I mentioned above was running without boost where you get constant 950 mm HG wide throttle setting band from 72%-100%.

[CountZero]

If there is nothing wrong with how supercharger works in game, then they need to fix specifications for it as 3500m is not altitude in game at what you should switch to stage 2.

It should say that if your in combat engine mode you should switch at 4500m to stage 2, and if your in boosted mode you should switch at 2500m to stage 2, as this is how it works best in game. And that would be realy special engine in game or real world if it worked how it works now in game. Its clear bug.

For any other airplane in game if spec say switch to stage 2 at certen alt, that is best alt to switch to it in game also, only la5s engine has this error.

Edited September 29, 2019 by 77.CountZero

[-=PHX=-SuperEtendard]

4 hours ago, 77.CountZero said:

And that would be realy special engine in game or real world if it worked how it works now in game.

 

it is correct behaviour, if you have different engine settings at the same RPM and the same supercharger, for each power setting there is a different optimal switching altitude.



Notice how in this P-51B speed chart the optimal supercharger switch altitude when using 75" is 12400 feet, but with 67" it's higher at 15500 feet and with 61" it's at 18200 feet.

So yes it is expected that the La-5 needs a lower supercharger gear switch altitude when using the boost mode. What I am not sure if it's correct is if the La-5 is supposed to use the boost in the second supercharger gear, afaik it's wasn't allowed?
 

[SCG_Limboski]

4 hours ago, 77.CountZero said:

If there is nothing wrong with how supercharger works in game, then they need to fix specifications for it as 3500m is not altitude in game at what you should switch to stage 2.

It should say that if your in combat engine mode you should switch at 4500m to stage 2, and if your in boosted mode you should switch at 2500m to stage 2, as this is how it works best in game. And that would be realy special engine in game or real world if it worked how it works now in game. Its clear bug. For any other airplane in game if spec say switch to stage 2 at certen alt, that is best alt to switch to it in game also, only la5s engine has this error.

 

For the La-5FN with the M-82FN engine, engaging the 2nd stage supercharger at 2,500m will decrease maximum level speed for any RPM and throttle settings of the same value (despite the second stage showing a higher MAP).  Where you referring to one of the engines (M-82 or M-82F) on the La-5 series 8?

 

The La-5s also do not have "combat mode" listed but only "nominal" and "boosted" too.

[JtD]

As you can see in the below chart, both the FN (1/4/7) and the F (2/5/8) engine lose power if you engage the 2nd gear at 2500m. Point 6 is the altitude at which you are supposed to switch charger, it's 3100 for the FN and 3600 for the F. At this altitude, both gears deliver the same power - above it, 2nd gear delivers more than 1st, below it, 1st delivers more than 2nd. This is true even though 2nd gear will produce full manifold pressure (1000mm / 950mm) at this altitude, while 1st gear delivers a lot less. It can only maintain the 1000mm/950mm up to altitudes of 1500m/2000m. Reason for this has been mentioned already, the 2nd stage of the supercharger consumes a LOT of extra power, in this case it needs about 300hp more than the 1st stage. This will only be offset by the added manifold pressure at higher altitudes. MAP just isn't everything.

 

[CountZero]

1 hour ago, SCG_Limboski said:

 

For the La-5FN with the M-82FN engine, engaging the 2nd stage supercharger at 2,500m will decrease maximum level speed for any RPM and throttle settings of the same value (despite the second stage showing a higher MAP).  Where you referring to one of the engines (M-82 or M-82F) on the La-5 series 8?

 

The La-5s also do not have "combat mode" listed but only "nominal" and "boosted" too.

my bad i ment there nominal/continues insted combat mode

 

1 hour ago, JtD said:

As you can see in the below chart, both the FN (1/4/7) and the F (2/5/8) engine lose power if you engage the 2nd gear at 2500m. Point 6 is the altitude at which you are supposed to switch charger, it's 3100 for the FN and 3600 for the F. At this altitude, both gears deliver the same power - above it, 2nd gear delivers more than 1st, below it, 1st delivers more than 2nd. This is true even though 2nd gear will produce full manifold pressure (1000mm / 950mm) at this altitude, while 1st gear delivers a lot less. It can only maintain the 1000mm/950mm up to altitudes of 1500m/2000m. Reason for this has been mentioned already, the 2nd stage of the supercharger consumes a LOT of extra power, in this case it needs about 300hp more than the 1st stage. This will only be offset by the added manifold pressure at higher altitudes. MAP just isn't everything.

 

in game if you turn sup 2 abow 2,5km in la5 you gain more speed with boost on

spawn at kuban autum in qm at 3km, and if on sup 1 in boosted mode i get 497kmh ias, and in sup 2 501kmh IAS, so its not like spec in game say 3500m to switch its abow 2500m then. Even the game starts you in air with sup 2 activated at 3000m in qm.

While in nominal/continues mode i get 470kmh ias on sup2, and 498kmh ias in sup1 at 3000m.

So its faster on sup 1 and nominal mode, then on sup1 and bosted mode on same alt of 3000m. From what i can see if on la5 your flying in nominal best is to keep sup1 up to 4,5km, and if in boost mode best is to switch to sup 2 abow 2,5km, and not like in game spec say 3,5km. So its either spec wrong or engine behavior, both cant be correct.

Edited September 29, 2019 by 77.CountZero

[Matt]

In level flight you get extra manifold pressure due to ram air in gear 1, so the altitude at which you should switch gear for higher speed is a bit higher. In a climb, the 3500 meters should be more or less correct (also depends on climb speed).

 

What is strange about the La-5 is that you gain extra performance by using boost even in second gear. Afaik, the "boost mode" should only work in gear 1. But i've not gotten a response back when that was introduced (which was a couple of years back). I still think that's bugged.

[JtD]

According to the chart, 2nd stage comes without the option for use of 'boost mode'. According to the manual, it was technically possible, but could lead to "detonation, loss of power and increased wear" and therefore forbidden.